1. Field of the Invention
The invention relates in general to a method of fabricating a semiconductor device, and more particularly, to a method of increasing the contact area of contact window using local oxidization.
2. Description of the Related Art
At present, in many highly integrated semiconductor devices, more than two levels of interconnecting metal layers are necessary to form a three dimensional network, called mutilevel metal interconnects (MLM), because of the increasing integration density of semiconductor devices. In the first level, the metal line is commonly polysilicon or metal, which can be electrically connected by contact plugs to a device.
In the conventional method, first the transistor is formed in the active region insulated by a field oxide (FOX). Then, the substrate is covered by an insulator, and the contact plug is formed in the insulator and connects to the source/drain of the transistor.
In the contact interface between contact plug and substrate, junction resistance induced by the contact of different materials results in slowing the transmission of the electric current. The larger the junction resistance and the longer the resistance-capacitance time delay, the slower the electric current transmits.
In the integrated circuit technology at the deep sub-micron level, the planar area which can be used by the contact plug is continuously decreasing and the contact area of the contact window is decreasing, as well. Thus, in this situation of increasing junction resistance, a method which can promote the operation quality of the device, reduce the contact resistance and resistance-capacitance time delay, and effectively increase the contact area without increasing the planar area is demanded.
Therefore, the purpose of the invention is to provide a method which can meet the requirements described above, without adding extra steps to the process.